Thank you very much for providing that information! Based on the clarifications you sent in, I'd like to gather a few more details related to your network. As a quick next test, if it's possible on this machine, please connect to an alternate network that you know does not contain strict security like the current network you're on, and then check to see if your connection with Craft works on that network. If it does, we know there is most certainly some form of Firewall or Network block of some kind on that network preventing proper network connectivity with Craft.

In that case, I would ask that you confirm the Proxy settings that you have set up within this network on your machine. Additionally, if you could also provide further details of an anti-virus software that you may be running on this machine, as they can often block certain network ports or overall domains (which is used when connecting with Craft), that'd be great.

Although it does not appear that this trouble is directly related to an outdated Sync plugin, I'd like to also get further confirmation of the version of the Craft Sync plugin specifically that you're working with.

I know this is quite a lot of information, but I really appreciate you taking the time to work with me on this matter. I look forward to hearing back from you with further updates.